The adult uterus undergoes repeated cycles of injury and repair in response to hormonal signals during the estrous cycle in mice (or the menstrual cycle in primates) numerous times in a normal mammalian reproductive lifespan, as well as during pregnancy when it grows ten-fold to accommodate the fetus. Although this process of remodeling is essential for reproduction, the molecular mechanisms involved are largely unknown, particularly in primates where the top layer of the endometrium is shed and regenerated every month. The principal investigators have shown that conditional deletion of ?-catenin in the Mullerian duct mesenchyme results in a progressive replacement of uterine smooth muscle cells in the myometrium with adipose tissue. They have also shown that the converse experiment with conditional expression of a gain-of-function allele of ?-catenin results in myometrial smooth muscle hyperplasia and development of stromal sarcomas and leiomyoma's (uterine fibroids). Both phenotypes were observed only after mice entered sexual maturity, suggesting that the mechanisms disrupted in these mice are regulated by ovarian steroid hormones. The principal investigators hypothesize that disruption of the nuclear function of ?-catenin, a key determinant of stemness in many stem cell microenvironments, in myometrial stem cells leads to these uterine pathologies. They have identified the regenerative myometrial smooth muscle stem cells in mice and in humans and propose to investigate whether endocrine disruptors (1) impact the differentiation and pluripotency of myometrial stem cells in vitro and in vivo during cycling, pregnancy, and leiomyoma development; (2) dysregulate the molecular mechanisms of Wnt/?-catenin signaling in our gain-of-function and loss-of-function models; and (3) alter the differentiation and pluripotency of myometrial stem cells during the perinatal window of myometrial development. The results of these experiments will help determine whether endocrine disruptors have a significant impact on the differentiation and function of myometrial stem cells. Performing these experiments in unique mouse models of dysregulated Wnt/?-catenin signaling will also help determine which of the molecular mechanisms used by ?-catenin, during normal and conditionally disrupted differentiation and in the adult activities of the myometrial stem cells, are affected. The principal investigator predict that an environmentally relevant level of exposure to endocrine disruptors plays an important role in uterine biology, particularly at the myometrial stem cell level and its contribution to uteine fibroid etiology and pathophysiology.